Sump spaces?

[mark]

Depending on your lights, pumps etc, may need something to keep your temperatures down and evaporation is one of the easiest ways. Other way is a chiller but they can be costly. Not sure of your system but might not be a whole lot of evaporation. I've got about 200G system total, couple of external pumps, internal on the skimmer and 2-250W MH and evap 1-2g a day.

There is nothing wrong with lids if you keep your temps okay. You can try running with temporary lids and if no problems, look to something more permanent later.

About the only negative is salt creep. With a lid on the tank you can have problems such as the lid blocking light, could consider a hood though. Air exchange is another thing but a skimmer can help. Not sure of the height of you skimmer so maybe harder to make your sump tight. A bit of gap isn't a big deal.